Coil forming system having an expandable mandrel

ABSTRACT

A coil spring forming system includes a mandrel having at least a portion that is selectively expandable so that a central portion of a resulting coil spring has a larger dimension than reduced diameter end sections of the spring. In one example, a plurality of coil shaping surfaces are supported relative to a central portion of the mandrel using a plurality of linkages. The coil shaping surfaces are moved using an actuator (i.e., hydraulic or pneumatic) between expanded and contracted positions to selectively vary the largest outside dimension of the mandrel. In one example, the coil shaping surfaces are spaced apart from each other in the expanded position. In another example, the coil shaping surfaces are arranged such that the mandrel has a generally continuous outer periphery when the surfaces are in the expanded position.

BACKGROUND OF THE INVENTION

[0001] This invention generally relates to forming coil springs. More particularly, this invention relates to a system including an expandable mandrel for forming coil springs having reduced diameter end sections at both ends of the coil.

[0002] In many instances, it is desirable to have reduced diameter ends on a wound coil spring. One example application for such springs is in automotive suspension systems.

[0003] In a typical coil spring forming manufacturing method, a cut-to-length bar is wound around a solid mandrel that sets the inside diameter of the coil spring. One end of the spring can be formed smaller than the rest of the spring using this technique. A reduced diameter at one end of the spring can be beneficial for efficiency in spring height and operating travel. The mandrel for such springs typically has a smaller diameter on one end to form the reduced end of the spring.

[0004] It is also beneficial in many circumstances to reduce the diameter of the second end of the spring for similar size and performance reasons. Given current manufacturing methods, however, this is not possible to complete within a single forming operation. Using a conventional technique, the second, reduced end of the spring would prevent the mandrel from being removed from within the spring. A secondary operation is required.

[0005] Requiring a secondary operation increases the overall production cycle time, which corresponds to lower manufacturing efficiency. Additionally, the time that the spring remains outside of a quench both after the initial forming step can have detrimental metallurgical results. Similarly, the additional handling of the hot spring during the secondary forming operation increases the possibility that the spring surface can be marked, which can lead to a stress concentration and potential early fatigue of the spring in service. Another disadvantage to conventional methodology is that the number of reduced turns on the second formed end is limited because of the fixturing and tooling issues involved in the secondary operation.

[0006] There is a need for an improved coil spring forming approach that allows for reduced ends to be formed on each end of the spring during a single coil forming, winding operation. This invention meets that need while avoiding the shortcomings and drawbacks of the prior art.

SUMMARY OF THE INVENTION

[0007] In general terms, this invention is a device for making a coil spring that has reduced diameter end sections at both ends of the spring, using a single forming operation.

[0008] A device designed according to this invention includes a selectively collapsible mandrel that has a plurality of coil shaping members supported to be selectively moveable between a first position where at least a portion of the mandrel has a first outside dimension and a second position where the mandrel has a second, smaller outside dimension.

[0009] By selectively moving the coil shaping members into the necessary positions, a coil spring having reduced diameter ends at both end sections can be formed. The mandrel coil shaping members can then be contracted into a collapsed position so that the mandrel can be removed from within the coil even with reduced diameter end portions at both ends of the spring.

[0010] In one example, the coil shaping members are arranged such that in the expanded condition, there is no contact between them while in the reduced diameter position, the coil shaping members contact each other. In another example, a generally continuous circumference is provided in the expanded position and at least a portion of at least one of the coil shaping members folds or collapses so that the mandrel can assume the second, reduced diameter outside dimension.

[0011] The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 schematically illustrates a system for forming coil springs designed according to this invention.

[0013]FIG. 2 schematically illustrates one example mandrel designed according to this invention in a first operating position.

[0014]FIG. 3 is a cross sectional illustration taken along the lines 3-3 in FIG. 2.

[0015]FIG. 4 schematically illustrates the example of FIG. 2 in a second operating position where the mandrel has a reduced outside diameter.

[0016]FIG. 5 is a cross sectional illustration taken along the lines 5-5 in FIG. 4.

[0017]FIG. 6 schematically illustrates another example mandrel designed according to this invention.

[0018]FIG. 7 is a cross sectional illustration taken along the lines 7-7 in FIG. 6.

[0019]FIG. 8 is a schematic illustration of the embodiment of FIG. 6 in a second operating position where the mandrel has a reduced outside dimension.

[0020]FIG. 9 is a cross sectional illustration taken along the lines 9-9 in FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021]FIG. 1 schematically illustrates a coil spring forming system 20 for making coil springs 22 out of coil stock 24. The preferred arrangement facilitates forming a coil spring 22 having reduced diameter end sections at both ends of the coil using a single coil forming or winding procedure so that no secondary processing is necessary to achieve a reduced diameter end section at both ends of the coil spring 22.

[0022] The coil stock 24, which can be a conventional steel rod, for example, preferably is heated in a conventional manner in a heating station 26. The heated coil stock preferably is then transferred to a forming portion 26 of the system 20. The illustrated example includes a lead screw 28 that operates in a conventional manner to conform the heated coil stock to a mandrel 30 while controlling the pitch of the coil spring. After the coil is sufficiently formed, it is removed from the mandrel 30 and cooled in a conventional manner in a cooling station 32. One example cooling station includes a quench bath where the heated, wound coil stock is immersed and appropriately treated to provide the desired resulting coil spring characteristics.

[0023] Because the coil spring 22 has reduced diameter end sections at both ends of the coil, the mandrel 30 is significantly different than conventional mandrels. The mandrel 30 has at least a portion that is selectively expandable to establish the larger diameter central portion of the coil spring. The mandrel portion is also selectively retractable into a position where the mandrel has a reduced outside diameter so that it can be removed from the coil spring 22, even though the end portions at both ends of the coil spring are reduced compared to the dimension of the central portion.

[0024]FIG. 2 schematically illustrates one example mandrel designed according to this invention. The mandrel 30 includes a plurality of coil shaping surfaces 42 that are selectively moved into a first position (as illustrated in FIGS. 2 and 3) where at least a portion of the mandrel has a first outside dimension. In this expanded position, the coil shaping surfaces 42 establish the larger diameter of the central longitudinal portion of the coil spring 22. The ends of the mandrel 30 preferably are tapered according to the requirements for the reduced diameter end sections of the coil spring.

[0025] After the coil spring has been formed about the mandrel 30, the coil shaping surfaces 42 preferably are collapsed or retracted into a second position where the outside diameter of the mandrel has a second, smaller dimension. This is illustrated schematically in FIGS. 4 and 5, for example. In this position, the largest outside dimension of the mandrel is small enough so that the coil can be removed from the mandrel even though the ends of the coil have a reduced dimension compared to the central portion of the coil.

[0026] As can be best appreciated from the cross sectional illustrations in FIGS. 3 and 5, the mandrel 30 includes a central portion 44, which may be a solid post made from steel or another suitably hard material. A plurality of linkages support the coil shaping surfaces 42 relative to the central portion 44. The linkages 46 facilitate movement of the coil shaping surfaces 42 between the first and second positions to establish the desired outside dimension of the mandrel 30.

[0027] In one example, a controller 48 controls movement of the linkages 46 to establish a desired outside dimension of at least a portion of the mandrel 30. The outside dimension in one example is selectively controllable to be varied to accommodate different coil spring configurations. The controller 48 in one example includes a microprocessor that is programmed to control the operation of the linkages 46 to achieve the desired mandrel position and the corresponding coil spring configuration. In another example, the controller 48 includes a hydraulic actuator for providing the motive force to move the coil shaping surfaces 42 between the expanded and collapsed positions. In another example, the controller 48 includes pneumatic power. Given this description, those skilled in the art will be able to select from among commercially available components or to custom design such components to achieve an arrangement that is sufficient for moving the coil shaping surfaces and supporting them in the positions needed during a coil forming procedure.

[0028] Another example is shown in FIG. 6 where a plurality of coil shaping surfaces 50 and 52 are in contact with each other when the mandrel 30′ is in a fully expanded position. The example of FIGS. 2 through 5, included spaces between the coil shaping surfaces 42 when the mandrel was in the expanded, first operating position. In the example of FIGS. 6 through 9, the coil shaping surfaces form a more continuous outer periphery when the mandrel is in the expanded position.

[0029] As best appreciated from FIGS. 7 and 9, the coil shaping surfaces 50 and 52 are supported by linkages 54 so that they are moveable relative to a central portion 56 of the mandrel 30′. A plurality of hinges 60 couple appropriate ones of the coil shaping surfaces 50 to a corresponding set of coil shaping surfaces 52. In the expanded condition (illustrated in FIGS. 6 and 7), the coil shaping surfaces 52 are moved outward relative to the axis of the mandrel and rotated about the hinges 60 into the position shown in FIG. 6 and 7. In the collapsed position, the coil shaping surfaces 52 are not only drawn radially inward toward the central axis of the mandrel 30′, but are also folded relative to the coil shaping surfaces 50 about the pivot axes of the hinges 60. Such an arrangement provides for a more continuous outer periphery of the mandrel when the coil shaping surfaces 50 and 52 are in the expanded position.

[0030] A variety of configurations are within the scope of this invention that permit for a relatively continuous outer periphery of the mandrel when the coil shaping surfaces are in the expanded positions.

[0031] In one example, the coil shaping surfaces 42, 50 and 52 comprise steel. In another example, a suitably hard substitute material is used. Given this description, those skilled in the art will be able to select from among commercially available materials to achieve the desired performance of a mandrel for a particular application.

[0032] The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this invention. The scope of legal protection given to this invention can only be determined by studying the following claims. 

We claim:
 1. A device for making a coil spring, comprising: a selectively collapsible mandrel having a plurality of coil shaping members supported to be selectively movable between a first position where at least a portion of the mandrel has a first outside dimension and a second position where the mandrel has a second, smaller outside dimension.
 2. The device of claim 1, wherein the mandrel has a central portion and the coil shaping members are supported by linkages between the central portion and the shaping members and wherein the linkages are selectively movable to change the outside dimension of the mandrel.
 3. The device of claim 1, wherein the mandrel has a central portion and the coil shaping members are supported to be movable relative to the central portion and including link members associated with the shaping members, the link members being one of hydraulically or pneumatically actuated to cause movement of the shaping members relative to the central portion.
 4. The device of claim 1, wherein there is arcuate spacing between the shaping members when the shaping members are in the first position.
 5. The device of claim 4, wherein the shaping members contact each other in the second position.
 6. The device of claim 1, wherein the shaping members form a generally continuous periphery about an outer surface of the mandrel in the first position.
 7. The device of claim 6, wherein at least one of the shaping members moves into a folded position as the shaping members move into the second position.
 8. The device of claim 1, wherein the mandrel has longitudinal ends and the outside dimension of the mandrel near the ends is smaller when the shaping members are in the first position than the outside dimension at a longitudinally central portion of the mandrel.
 9. The device of claim 1, wherein the first outside dimension varies along the length of the mandrel.
 10. The device of claim 1, including a lead screw associated with the mandrel such that the lead screw and the mandrel cooperate to form a coil from a metal rod by causing the metal rod to conform to the shape of the mandrel provided by the shaping members such that at least a portion of the coil has an inside dimension corresponding to the first outside dimension of the mandrel.
 11. The device of claim 1, wherein the shaping members each have a longitudinal length that is shorter than a longitudinal length of a coil shaping surface of the mandrel.
 12. The device of claim 1, wherein the shaping members each comprise steel.
 13. A method of making a coil spring using a mandrel, comprising the steps of: (A) placing the mandrel into a first operative position such that an outside dimension of the mandrel corresponds to a desired inside dimension of the coil; (B) wrapping a metal rod around the mandrel to thereby form the coil; (C) reducing the outside dimension of at least a portion of the mandrel; and (D) subsequently separating the coil from the mandrel.
 14. The method of claim 13, wherein the outside dimension of the mandrel is greater near a longitudinal center of the mandrel than near longitudinal ends of the mandrel when performing steps (A) and (B).
 15. The method of claim 13, wherein step (A) includes providing a coil shaping surface around an entire periphery of the outside of the mandrel.
 16. The method of claim 15, wherein step (C) includes folding at least one of the coil shaping surfaces into a collapsed position.
 17. The method of claim 13, wherein step (A) includes providing a coil shaping surface at selected intervals around a periphery of the outside of the mandrel. 